Utilizing in vitro techniques, steroid and estrogen sulfotransferase activities will be determined in porcine uterus throughout the estrous cycle and, following fertilization, these enzymic activities will be ascertained during the process of implantation. Throughout these investigations nuclear estrogen migration will be followed by the H3-estradiol exchange method. It is anticipated that data will be obtained from these experiments which will be useful in understanding the importance of the above metabolic parameters in uterine reproductive function. In order to relate these findings to human reproductive biology, it is our intention to examine human endometrial curettings (or whole uterine tissue), obtained at various phases of the menstrual cycle, for the described sulfotransferase activities and nuclear migration of H3-estradiol.